1. Field of the Invention
The present invention relates to an induction-heated roller device.
2. Description of the Related Art
As well known, the induction-heated roller device is provided with an induction heating mechanism disposed within a rotary roll. The induction heating mechanism includes an iron core and induction coils wound on the iron core. The induction-heated roller device will be described with reference to FIG. 5. In the figure, reference numeral 1 is a roll, and the roll is rotatably supported on a frame 2 by means of a bearing 3, and driven to rotate by a drive source (not shown). Reference numeral 4 is a jacket chamber which is formed in a thick part of the roll 1 and is filled with a two-phase (gas and liquid) heating medium.
An induction heating mechanism 7, located within the hollow space of the roll 1, includes a plurality of induction coils 5 and an iron core 6 wound with the induction coils. Reference numeral 8 indicates magnetic discs each interposed between the adjacent induction coils, and reference numeral 9 indicates a support rod for supporting the induction heating mechanism 7. The support rods 9 are respectively supported within journals 11 coupled to the roll 1 through bearings 10. Reference numeral 12 represents lead wires 12 of the induction coils 5, and those wires are led out to exterior through the support rod 9, and is connected to an AC power source located outside.
A three-phase power source is used for exciting the induction coils. The reason for this is that such a power source is readily available. As well known, a phase difference among the U-, V- and W-phase voltages of the three-phase power source is 120xc2x0. Accordingly, three induction coils are used. When the phase voltages are applied to those induction coils, two roll surface areas which are located between the adjacent induction coils while facing the latter, as known, is lower in temperature than the remaining roll surface.
The temperature may be decreased by reducing the phase difference between the voltages applied to the adjacent induction coils. An approach to realize this is proposed in which a three-phase voltage is used as a primary voltage, a multiphase transformer more than four phases is used, and the secondary voltages are applied to more than four induction coils (Japanese Patent Unexamined Publication No. Hei. 9-7754).
In this approach, a phase difference between the voltages applied to the adjacent induction coils may be reduced to be smaller than 120xc2x0. Therefore, the local temperature decrease on the roll surface may be lessened when comparing with the case where the three-phase voltage is directly applied to the induction coils. However, this approach indispensably uses the multiphase transformer. Accordingly, the cost to manufacture is increased, and a space to install the multiphase transformer is secured.
Accordingly, an object of the present invention is to provide an induction-heated roller device which when a power source is a three-phase power source, and voltages whose phases are different from each other by 30xc2x0 are applied, as exciting voltages, to adjacent induction coils of twelve induction coils disposed within a hollows space of the roll, the exciting voltages having phase differences of 30xc2x0 may be applied to the induction coils by using only the connection of the induction coils, without the multiphase transformer.
According to the present invention, there is provided an induction-heated roller device having a rotary roll, twelve induction coils for an induction heating mechanism being successively disposed within a hollow space of the roll while being spaced apart in an axial direction of the roll within a hollow space of the roll, a three-phase power source for exciting the induction coils. The induction-heated roller device is improved such that the induction coils being arranged into: a first group of three delta connected induction coils excited by line voltages of the three-phase power source; a second group of three star-connected induction coils being excited by the line voltages and being spaced apart in a phase rotation direction of the first group of induction coils; a third group of three delta-connected induction coils being excited by phase-shifted voltages formed by phase-shifting voltages of the three-phase power source by 180xc2x0 and being spaced apart in a phase rotation direction of the second group of induction coils; and a fourth group of three star-connected induction coils being excited by the phase-shifted voltages and being spaced apart in a phase rotation direction of the third group of induction coils. The induction-heated roller device may further comprises an x number of induction coils (x: an integer of 1 or greater) connected in parallel with any of 1 to 12 of the twelve induction coils. The induction-heated roller device may also be constructed such that any of 5 to 11 induction coils are selectively located at the positions at which the twelve number of induction coils are to be located and are connected so that a phase difference of the voltages applied to the induction coils is 30xc2x0.
The voltages are sequentially applied to the induction coils at a phase interval of 30xc2x0. This voltage application is equivalent to the application of the secondary voltages of the multiphase transformer. It is realized by using only the connection of the induction coils, and hence in this respect, there is no need of the multiphase transformer.